Depends on the frequency of deals.

Recommendations for frequency of calls?

One would think the city would go after them but as of two years ago I was told the city wasn't doing anything about it (my city also had over a million dollars in unpaid parking tickets but they're finally beginning to boot cars with some frequency so hopefully they get on the bad landlords as well).

And at what frequency? 

The frequency at which that is conducted is determined by the county. 

Also, if you overindulge them with these little things, sometimes instead of pacifying them, it increases the frequency with which they call you about minutiae. 

And you would have a better ROI.You can send a nice mailer all in for 60c-$2.40 or ramp up your frequency to a targeted list and get better results.

So "constantly" is subjective in terms of inquiry frequency. 

Your message may be tired, your market may have shifted, your mail piece may be boring or your audience is fatigued by your frequency (the "Magic Jack" syndrome).  

Should you be classified as a dealer, you are deemed to be in an active trade or business and will be taxed at ordinary income rates plus self-employment tax.When you look at how the IRS examines a "dealer" one of the most important issues appears to be the taxpayer’s volume, frequency and consistency of real estate sales.